Electronic status determining label

ABSTRACT

An activatable, and deactivatable electronic status determining label of ferromagnetic construction, and broad application, in tagging objects to permit selective detection of tagged objects depending upon the activation state of the label. The label comprises a thin, layered structure of any size and shape having a central layer of ferromagnetic substance sandwiched between two thin non-magnetic covers. The activated state is derived by producing a multiplicity of magnetically saturated lines, or grooves, in the ferromagnetic substance, each of which is magnetically biased to receive and momentarily store radiant energy from an interrogating read-out zone and return same to the zone in a form characteristic of the label. The deactivated state is derived in two ways: by removing the saturation lines from the ferromagnetic substance, using well-known de-magnetization technics; or by adding a great multiplicity of crossing lines of magnetic saturation and thus breaking the ferromagnetic substance up into a multiplicity of small inactive uncoordinated areas.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division applicaton of U.S. Patent Application,Ser. No. 735,070 filed Oct. 22, 1976, now U.S. Pat. No. 4,158,434 whichwas filed as a continuation-in-part of U.S. Patent Application, Ser. No.874,760 filed Nov. 7, 1969, now U.S. Pat. No. 4,055,746.

FILED OF INVENTION

The invention relates generally to a ferromagnetic memory element in theform of a label, card, tag, coupon or marker in a system for detectionof the memory element to prevent unauthorized removal of objects havingthe memory element attached thereto.

DESCRIPTION OF THE PRIOR ART

There are in existence several systems for detecting or preventing thetheft of articles of value. One of these described in U.S. Pat. No.3,754,226, granted to E. R. Fearon, Aug. 21, 1973, entitled "Open-StripFerromagnetic Marker And System For Using Same," described an improvedmarker and system. This marker, when secured to an object, enablesdetection of the presence of the object when the object is in aninterrogation zone, such as a doorway, when the zone has a magneticfield varying at a pre-determined fundamental frequency. This markerutilizes an elongated ferromagnetic marker of low coercivity capable ofgenerating a detectable signal containing harmonics of the fundamentalfrequency when placed in the zone. An improvement to this inventiondescribed in U.S. Pat. No. 3,747,086, granted to Glen Peterson July 17,1973, entitled "Deactivatable Ferromagnetic Marker For Detection OfObjects Having Marker Secured Thereto And Method And System Of UsingSame," adds an element of high coercivity to the element of lowcoercivity whereby the magnetized, or unmagnetized, state of the highcoercivity element controls the ability of the low coercivity element togenerate and radiate harmonics of the interrogating signal. Thisimprovement makes it possible to determine, with considerable precision,whether or not the goods passed, or carried, through the interrogationzone are being properly removed or whether the passage is illicit.

A somewhat, earlier system for detecting or preventing the theft ofarticles corresponds with U.S. Pat. No. 3,292,080, granted to E. M.Trikilis, Dec. 13, 1966, Makes use of a magnetometer in theinterrogation zone and utilizes a magnetized object which identifies thearticle unless check-out procedure has removed the magnetism from theobject.

French Pat. No. 763,681, issued to Pierre Arthur Picard, discloses aremote detection system which employs dynamic magnetic phenomena todetect the presence of an object. The system of Picard, which isfundamental to most of the useful ferromagnetic systems presently inuse, is based upon the discovery that a piece of metal subjected to asinusoidally varied magnetic field produces in a pair of balanced pickupcoils in the vicinity of the applied field an induced voltagecharacteristic of the metal. The Picard patent discloses that highpermeability metals produce an induced voltage including high orderharmonics of the sinusoidal field.

Additionally, in the area of ferromagnetic markers, the patent issued toRobert E. Fearon Dec. 22, 1971, U.S. Pat. No. 3,631,442; the patentissued to James T. Elder and Donald A. Wright May 23, 1972, U.S. Pat.No. 3,665,449; and the patent issued to James T. Elder Oct. 9, 1973,U.S. Pat. No. 3,765,007, make use of some of the foregoing and relatedphenomena.

All of the foregoing systems have severe difficulties of one kind oranother. The Trikilis system requires a rather large piece offerromagnetic material for the marking of the merchandise, otherwiseambient variations in the magnetic field are greater than the changescaused by the Trikilis marker. The Picard system does not provide ameans or deactivating the marker, nor does it provide a means ofsufficient sensitivity to uniquely identify particular markerconstruction as opposed to other ferromagnetic materials. While thecombined systems of E. R. Fearon and Glen Peterson, above referenced,together provide great sensitivity and a means of deactivating themarker, they require a very specific marker construction whereby onedimension of the marker, as the length, is very large compared with theother two dimensions of the marker, as the width and thickness. Similarrequirements can be found in the methods used by J. T. Elder and DonaldA. Wright.

SUMMARY OF THE INVENTION

In this application, as in the application of which this is a part, andin all applications which have been divided from the originalapplication, above referenced, a computer is any instrumentality whichautomatically stores, assimilates and processes information of any kindwhatsoever, makes a register of results for visual use by people,compares presently taken data with that previously taken, rings a bell,flashes a light, closes or opens a door, or operates another machine.

While the bits of digital information used in and stored by computersare usually made as physically small as possible so that a maximum ofinformation can be stored in a minimum volume of space, and while themost modest of computers will require thousands of bits, the preferredembodiment of this invention requires only two bits of information andthese bits must preferably occupy large volumes of space as comparedwith the more usual bit. Whereas, the usual computer bit is read inclose proximity to the computer reading apparatus, the bit of thisinvention must usually be read in an open doorway considerably removedfrom the closest other piece of computer apparatus, and this accountsfor the comparatively large physical size required of the bit.

Again, the usual computer is permitted to make contact, in one way oranother, with the substance carrying the bit of information as it isread, or at least be so close to the substance that contact could bemade if it was desirable to do so. The present invention comprises anon-contact method of and system for distinguishing the presence, statusand identity of an object by determining which of two bits ofinformation are stored in a remote element or a label attached to theobject. One bit, as interpreted by the computer and the manner in whichit is programmed, advises that the object is being legitimately movedthrough a doorway, or other form of interrogation (reading) zone; theother bit, as interpreted by the computer, advises that the object isbeing illegitimately moved through said doorway or interrogation zone.When the first bit is read, the computer is programmed to do nothing orat least no more than advise an observer that the passage of the objectis legitimate. When the second bit is read, the computer is programmedto sound an alarm, close and lock a door, or at least advise an officerthat the passage of the object is illegitimate.

Most of the practical anti-pilferage systems in use today employferromagnetic marker strips which can be activated and deactivated.These strips are usually long and thin, a construction that adapts themto radiate high-order harmonics of an interrogating signal unless means,called deactivation, are taken to break-up the length or otherwise clampthe marker magnetically. While long skinny strips are useful in markingand identifying some good items, for example--books, they are not soreadily adaptable to other goods items, for example--clothing.

It is usually desirable to associate the ferromagnetic marker with themanufacturer's label. Customers are adapted to accepting manufacturer'slabels and price tags but usually object to other extraneous materials.Particularly, are long strips of foreign matter objectionable inexpensive articles of clothing; moreover, it is usually desirable tohave the markers hidden or camouflaged so that the prospectiveshoplifter is not aware of their presence. For these reasons it ishighly desirable to combine the ferromagnetic marker with themaufacturer's label, price tag, etc. At the same time, these labels andprice tags usually have ordinary rectangular, circular or oval shapessuch that lengths and widths are not radically different, and in theseconfigurations they do not efficiently produce and radiate highorderharmonics of the interrogating signal or otherwise be disposed to anunique reading in an open doorway.

The object of this invention is to provide a ferromagnetic memoryelement, label, or marker tag, having an usual shape and size, and whichin one mode of activation is an efficient receiver and radiator ofresponses to an interrogating signal, and which, in another mode ofactivation or deactivation, is an inefficient generator and radiator ofresponses to interrogating signals.

It is a well-known fact in sound and video recording that biases greatlyenhance the ability of magnetic tapes to record signals with a minimumof noise and signal distortion. Both dc- (direct current) and ac-(alternating current) biasing have been used successfully. In theformer, a bias of sufficient strength is applied to the tape tomagnetically saturate it in one direction. An auxiliary winding in therecording head is then used to bring the tape back to an exact magneticneutral, and in this condition the signal to be recorded is applied. Thereason for doing this is that magnetic saturation, in one direction orthe other, is a more sure point of departure than the random neutral theparticles of the tape might happen to be in.

In the second form of biasing, a high frequency ac-bias of sufficientstrength to magnetically saturate the particles of the tape in eitherdirection is applied. The bias frequency is several times higher thanthe highest frequency to be recorded so that the applied signals inessence modulate the high-frequency bias after the manner of a carrierin radio-frequency techniques. This type of recording is almost noiseand distortion free and is the one most used today.

While neither of these methods are adapted specifically into thisinvention, they are here referenced to establish the fact thatferromagnetic materials can, and have been, biased in a multiplicity ofways for certain purposes, thus avoiding the necessity of establishingexperimentally or theoretically the conceptions that will be employedsubsequently in this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a drawing in plan view of a typical memory element label thatis attached to an object of commerce such as a suit of clothes.

FIG. 1b is an edge view, in elevation, of the memory element of FIG. 1a,disclosing the three essential parts.

FIG. 2a is an enlarged cross-section of a preferred form of recordingmedium used in the construction of the memory element of FIG. 1b.

FIG. 2b is an enlarged cross-section showing another construction forthe ferromagnetic substance used in FIG. 1b.

FIG. 2c is an enlarged cross-section showing a third form ofconstruction for the ferromagnetic substance used in FIG. 1b.

FIG. 3 is a schematic drawing showing the electrical conductor patternin relation to a typical memory element and label whereby theferromagnetic memory substance of the label is prebiased or activated.

FIG. 4 is a schematic drawing showing an alternative conductor patternin relation to a typical memory label whereby the ferromagneticsubstance of the label is activated.

FIG. 5 is a drawing in cross-sectional view showing the magnetic fieldpattern about one of the biasing conductors of either FIG. 3 or 4whereby the biasing, or activating, magnetic saturation pattern isestablished in the ferromagnetic memory substance.

FIG. 6a is a plan view showing the placement, and construction of, a setof conductors to bias or activate the ferromagnetic substance of amemory element or label, in one mode of operation.

FIG. 6b is an end view, in elevation, further disclosing the placementand construction of the set of biasing conductors of FIG. 6a.

FIG. 7a is a plan view showing the placement and construction of a setof conductors used to bias and activate the ferromagnetic substance of amemory element, or label, in another mode of operation.

FIG. 7b is an end view, in elevation, further disclosing the placementand construction of the set of biasing conductors of FIG. 7a.

FIG. 8 is a drawing in plan view showing the magnetic bias, oractivation, pattern that has been established in a typical memoryelement by the conductor biasing pattern of FIGS. 7a and 7b.

FIG. 9a is a drawing in plan view showing the placement and constructionof an additional set of biasing conductors used to slightly modify oradd to the magnetic biasing pattern of FIG. 8 whereby a pattern of greatlength and strength is established.

FIG. 9b is an edge view, in elevation, further disclosing the placementand construction of the biasing conductors of FIG. 9a.

FIG. 10 is a drawing in plan view showing the magnetic bias pattern thatresults from the combined actions of the conductor patterns of FIGS. 7and 9.

FIG. 11 is a schematic drawing in plan view showing how the activationbias pattern of FIGS. 5, 7, 8 and 10 is blocked by a cross-biasingnetwork and hence deactivated.

FIG. 12 is a schematic drawing in plan view showing how the activationbias patterns of FIGS. 4 and 6 is blocked by a cross-biasing network andhence deactivated.

FIG. 13 is a drawing in plan view of the activation-deactivation biasinghead which provides the conductor biasing patterns of FIGS. 6, 7, 9, 11and 12.

FIG. 14a is a plan view of a hand-operated stamp-like head used toactivate and deactivate status determining labels.

FIG. 14b is a view in elevation of the hand-operated, stamp-like head ofFIG. 14a.

FIG. 15 is a graph of the hysteresis loops of the materials used to formthe ferromagnetic memory substance by means of which the invention isfurther described and explained.

FIG. 15 is a schematic drawing of the read-out apparatus of thisinvention, or the interrogation zone as it is sometimes called.

FIG. 16a is a block diagram showing additional electronic units whichcan be added to provide an alternative method of label interrogation.

FIG. 17 is a schematic drawing in plan view of an alternative form ofdeactivation equipment that is used in practicing the present invention.

FIGS. 18, 19, 20 and 21 are graphs of some of the pulse forms which areapplied and which result in practicing the invention.

FIG. 22 is a drawing in plan view showing still another means of biasingor activating ferromagnetic memory labels.

FIG. 23 is a cross-section of the apparatus of FIG. 22, at AA', showingone of two arrangements of the activating conductors.

FIG. 24 is a side view, in elevation, of the apparatus of FIG. 22.

FIG. 25 is a cross-section of the apparatus of FIG. 22, at AA', showingan alternative arrangement of activating conductors.

FIG. 26 is a drawing in plan view which, in conjunction with FIG. 22,shows a magnet means of biasing or activating ferromagnetic memorylabels.

FIG. 27 is a cross-section of FIG. 26, at DD', showing the arrangementof magnetic poles in relation to the ferromagnetic memory label whichthey activate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Ferromagnetism is a rather complicated subject and much research hasbeen undertaken, and much written, to provide the understanding which wepresently have. For such an understanding we are obliged to refer to thebooks that have been written and even to original reports that are foundin numerous technical journals. For the purposes of understanding thisinvention perhaps a review of a few basic conceptions will suffice.

Iron and its oxides, from which we get the prefix "ferro," is one of thebasic elements exhibiting ferromagnetism. Nickel and Cobalt, which areclosely related to Iron in their atomic structures, also exhibitferromagnetic properties, and of particular interest are the alloys wehave learned to make of Iron, Nickel, Cobalt, Carbon, Aluminum,Platinum, Manganese, etc. Generally speaking, ferromagnetism is thephenomenon whereby certain electrically uncharged materials attract eachother. At one extreme, we have the hard permanent magnets with which allof us are familiar and with which most of us have toyed at one time oranother. At the other extreme, we have the soft `exotic alloys` which weuse in transformers, electric motors, microphones, recorders, andsimilar machines, and with which the average person is quite unfamiliar;nevertheless, their basic performance is essentially the same as that ofthe hard permanent magnet or P.M. The performance of both extremes, aswell as the thousands of examples therebetween, is described by what wecall a hysteresis loop. FIG. 15 shows the essential form of the twoextremes of ferromagnetism; the fat loop 132 describes the hard P.M.while the relatively skinny loop 131 describes the soft exoticmaterial--providing we understand that the scale along the abscissa, orH-axis, has been greatly contracted. If the hysteresis loops of theextremes of ferromagnetism were plotted in true scales, the drawingwould have to be many sheets of paper wide--that, or the hysteresisstructure of the most exotic alloy would be entirely hidden within thefinest straight line we can draw.

Ferromagnetic elements, compounds and alloys have atomic and molecularstructures which on a microscopic scale are responsible for the magneticproperties we perceive and use. To get at these properties and, ifpossible, improve them, we are limited, first of all, by the choice ofelements available to us; secondly, we are limited by the chemicalcompoundings we can make of the available elements; and thirdly, by themixtures (the alloys) we can make of the elements and/or their chemicalcompounds. With these selections made there is nothing in the world wecan do that will alter the microscopic properties of what we havecompounded or alloyed. Fortunately for us, however, there is a largerstructure within ferromagnetic materials available to us upon which wecan work, a macroscopic structure which we call the domain structure.

While very large compared with the structures of an atom or molecule,the magnetic domains of ferromagnetic materials are for the most partinvisible to the unaided eye. On polished surfaces they do sometimesbecome visible with the help of a simple optical microscope, and domainstructures can be made visible and studied with the help of x-rays,polarized light, polarized neutrons, electron beams, etc. Iron whiskers,however, and with which most who have played with P.M's. are familiar,contain very few imperfections and become aligned in an externalmagnetic field much as unseen domains do.

Once a ferromagnetic material has been derived or compounded, we areobliged thereafter to work with the domain structure in perfecting ourmachines. It is this structure which we arrange or alter when we heatand cool or `temper` magnetic allows; it is this structure which wealter when we mechanically rub, bend or otherwise cold-work aferromagnetic material. For example, the exotic properties of some ofthe best soft alloys can be lost or degraded by merely bending a stripof the material a few times over a sharp fulcrum. As a matter of fact,in the earliest days of these alloys before they were stabilized, merelydropping them to the floor would degrade them. Heating such alloys abovea certain point also usually destroys, or greatly alters, a desirabledomain structure or orientation. Again, heating and cooling in magneticfields is frequently used to obtain desirable and more-or-less permanentdomain alignments in ferromagnetic materials. Such alignments can,however, be temporarily obtained by the application of a magnetic fieldwithout the aid of heat. As a matter of fact, it is these alignments ofthe magnetic domains of a given piece of ferromagnetic material thatproduce its characteristic hysteresis loop.

Referring again to FIG. 15, we start at the origin, or point, O, intracing the original hysteresis loop, applying a MMF, or magneticdriving force along the +H axis, and move to the point A. With this muchapplied field, a domain with magnetization direction parallel to thefield direction has the lowest energy and the domain walls tend to moveto enlarge the volumes of favorably oriented domains. The magnetizationand favorable movement of domain walls increases as indicated by thecurve OAB. Over that part of the curve indicated by OA, or a littlebeyond, the domain wall motion is reversible; i.e., on the removal ofthe field the domain walls return to their initial positions. Uponapplication of higher fields as we move past arrow 142 toward B, at theapproach of the knee, the domain walls get displaced beyond theprevailing internal energy barriers so that when the MMF is removed, thedomain walls having stretched beyond their elastic limits no longerreturn to their initial positions; rather they trace out a curve, 133,which we call a minor hysteresis loop, and fall back to the point, C, onthe +B axis and in this condition they will remain until some magneticforce is applied that is great enough to produce wall motion and domainalignment, or mis-alignment, as the case may be.

If we continue to apply the MMF, i.e., the magnetic force along the+H-axis, instead of removing it a little beyond the arrow 142, we'llfollow the curve through point B, as indicated by the arrows 143 and144, beyond which no further magnetization of the material takesplace--no matter what MMF is applied. This means that the material ismagnetically saturated; i.e., all of the domains within the reach of theapplied MMF have become oriented in a direction parallel with theapplied field so that further alignment, or magnetization of thematerial, is impossible.

If we now remove the applied MMF, most of the domain structure derivedthrough saturation will be retained and the material will relax slightlyto the point, B_(r), and in this domain structure, which is far beyondthe reach of ordinary ambient temperature forces, it will remainindefinitely; i.e., until acted upon by some additional MMF, or otherphysical force sufficient to move or alter the structure.

In addition to the foregoing, there is some spontaneous domainorientation in ferromagnetic substances even in the absence of anapplied field. In the unmagnetized state, particularly in large bodies,the magnetic domains are oriented pretty much at random so that the netmagnetization of the whole body is zero. When, however, the body isrolled into thin sheets which is a typical form of fabrication forcommercial applications, it becomes easier for the domains to be alignedwith the directions of rolling so that we begin to get some domainorientation. When the thin sheets are cut into narrow strips we getfurther spontaneous domain alignment, and in long needle-like pieces thealignment is such that the needle behaves like a single domain and itrequires a considerable MMF to overcome or reverse the alignment. Thereis also a tendency, particularly in thin sheets and strips for strongdomains to spontaneously affect their neighbors, causing them to becomealigned in agreement. Thus, if spots of magnetic saturation are producedin thin sheets of ferromagnetic material by externally applied fields,there will be a tendency for these to spread or grow within thematerial, perhaps joining other spots, making a still strongermagnetization.

It is within the province of domain wall movements and structures thatthis invention is concerned.

FIG. 1, views a and b, shows a typical ferromagnetic memory element andmanufacturer's label, 1, in combination. 2 is the printed face of thelabel which is composed of paper, cloth, plastic, or other suitablenon-magnetic material and which is preferably very thin. 4 is theunprinted back of the label which, like 2, is composed of paper, cloth,or other suitable nonmagnetic material, but which, unlike 2, may beprovided with an adhesive surface for the ready attachment to objectsbeing marked and protected. 3 is a thin layer of ferromagnetic substancethat is sandwiched between 2 and 4. The label, 1, may be of any desiredsize and shape depending upon the application requirements of the trade;i.e., no particular specifications are placed upon its shape or size asis customary with other ferromagnetic markers.

FIG. 2a shows, in cross-section a construction for the memory elementlabel, 1, wherein the ferromagnetic substance, 3, is comprised of onethin layer of uniform magnetic material. 2 and 4, as before, are thecovering layers of non-magnetic material.

FIG. 2b shows, in cross-section, a memory element label, 1, wherein theferromagnetic substance is comprised of two thin layers, 5 and 6, offerromagnetic materials which have different magnetic properties. Forexample, 5 may be of ferromagnetic material that has relatively highpermeability and low coercivity, as 131, FIG. 15, while 6 may be aferromagnetic substance that has relatively low permeability and highcoercivity, as 132, FIG. 15. This combination of materials has certainuseful properties that will be brought out subsequently.

FIG. 2c shows a memory element label, 1, wherein the ferromagneticsubstance is comprised of three layers 7, 8, and 9, but usually of onlytwo ferromagnetic materials. For example, layers 7 and 9 will usually bethe same material and 8 will be a different material havingdistinguishing ferromagnetic properties compared with 7 and 9. Inanother application, 7 and 9 become materials having a high dielectricconstant which enhance the action of ferromagnetic layer 8. Detailsconcerning these applications will be given subsequently.

FIG. 3 shows schematically the series arrangement of biasing conductorsgenerally indicated by the arrow 10. 1 is the memory element labeldirectly beneath the biasing conductors; 11 is one terminal of thebiasing network, and 16 is the other terminal by means of which anappropriate EMF is applied to the network and currents flow therein asindicated by the arrows 12, 13, 14 and 15. As can be seen, currents flowin opposite directions in alternate legs of the biasing network andmagnetic fields established at right angles thereto, as shown in FIG. 5.

FIG. 4 shows schematically a parallel arrangement of conductors, 20,whereby currents flow in the same direction in all parts of the biasingnetwork, as indicated by the arrows 22, 23 and 24. Again, 1 is thememory element label, 21 and 25 are the terminals by means of which anEMF is applied to the network to produce a desired current flow.

Referring now to FIG. 5 which shows a typical cross-section of thememory element, 1, in the vicinity of one of the conductors 30 of eithernetwork 10 or 20. As before, 2 and 4 are the non-magnetic covering facesof the memory element 1, and 3 is the ferromagnetic substance sandwichedtherebetween. For simplicity of exposition, the conductor 30 is shown tohave a circular cross-section of diameter, d, but in actual practice itwill probably be a rectangular conductor of a printed circuit. Accordingto the law of Biot and Savart, the tangenital component of the magneticfield at the center of the ferromagnetic substance, produced by a flowof current in the conductor 30, will be ##EQU1## where

μ is the permeability of the ferromagnetic substance 3,

I is the magnitude of the current flowing in conductor 30, in abamps,

d is the diameter of 30, in centimeters,

a is the thickness of non-magnetic cover, 2, in centimeters

b is the thickness of the ferromagnetic substance, likewise incentimeters.

Accordingly, if I is only 1000, a rather nominal value; d=0.02 Cm.;a=0.01 Cm.; and b=0.02 Cm. ##EQU2## And if the saturation flux densityof the ferromagnetic substance is 6,700 gauss, a value appropriate tosome of the exotic alloys, a current of only 0.1 abamp=1.0 Prac. Amp.would be momentarily required to saturate such a ferromagnetic substancetangentially down to its center. Slightly more than this would berequired to saturate it all the way through. Currents of not more thanthree times this value would be sufficient to saturate the highestflux-density materials presently available. What is more, most of thematerials that would be used would have permeabilities greater than1,000 so that currents smaller than the above would be adequate in manycases.

When the biasing current is removed, the flux density in theferromagnetic material will fall back to its remanent value B_(r) orB_(R), as shown by FIG. 15, depending upon the kind of materialemployed, and here it will remain until acted upon by another magneticforce. It should be noted that the remanence value for a given magneticmaterial is one of the most sure and repeatable values the material has.If the conductors of the network of FIG. 4 are sufficiently closetogether, the entire body of the ferromagnetic substance, 3, will bemagnetized to the values B_(r) or B_(R), and in a directionperpendicular to the biasing conductor, or parallel to the lengthdimension of 1, as it is shown in FIG. 4. In this magnetically orientedcondition where all of the magnetic domains are appropriately organized,the memory element label, 1, for the purpose of this invention, is saidto be activated.

At this point in the exposition of this invention, it is appropriate torefer to the prior art, for a moment, where long needle-likeferromagnetic markers are preferred--indeed, required. The reason forthis, as already given, is that in long thin needle-like structures, themagnetic domains tend toward a self-alignment along the longestdimension and thereby pick up a magnetization. In this sense, the longedges of the ferromagnetic material provide domain aligningdiscontinuities. To keep a magnetic domain oriented perpendicularly to along edge, or discontinuity, requires more energy than is required fororientation parallel with the edge. Accordingly, the magnetic domainsadjacent the edges align themselves with the edges to meet the minimumenergy requirements of the material and those domains next to the edgedomains, as we move into the material, tend to align themselves with theedge domains so that in long, skinny strips of material there is ageneral magnetic organization of the material along the longestdimension. It is because of this magnetic domain alignment, ororganization, that long thin strips make useful ferromagnetic markers.When placed in an interrogating magnetic field, the strips readilyabsorb energy from that component of the field that is parallel to thelong dimension of the strip.

In larger sheets and bulk bodies of ferromagnetic materials, the onlyplaces where there is any spontaneous domain alignment whatsoever arethose adjacent an edge. Throughout the remainder of the material thedomains fall at random and so aren't organized to produce any particularresult. For these reasons, large sheets and bulk bodies of ferromagneticmaterials do not efficiently absorb and re-radiate the energy of aninterrogation zone; rather, the energy that is absorbed only adds to therandom motions of the magnetic domains and is lost in heat.

In the present invention, we are not limited by the edge alignments oflong thin strips; rather, we take the material provided in a memoryelement label, of whatever shape and size, and pre-organize itmagnetically by some suitable arrangement of electrical conductors, ormagnets, adjacent thereto and through which we drive a short pulse ofcurrent, or magnetic flux, respectively. The entire piece of materialthen becomes organized at a point of remanence and is thereforeactivated to receive and radiate energy in an interrogation zone.Because it saves material, avoids excessively thick and heavy andunattractive labels, and because it is desirable magnetically, we keepthe thin dimension of the ferromagnetic material but give completefreedom of artistic design to the other two dimensions.

Rather than drive an entire sheet into magnetic saturation by a currentsheet, and in so doing, provide a memory label that is less good thanwhat is possible, it is preferable to use discrete conductors at asuitable separation, as shown by FIGS. 6a and 6b. These conductorsshould be sufficiently close together, perhaps closer than shown, thatmore-or-less continuous paths of magnetic saturation are produced, andgood use is made of the material that is available. Since magneticfields are produced at right-angles to conductors carrying currents,some means must be provided to limit the magnetic field to discretepaths. The means employed by FIGS. 6a and 6b is that of a system of bentconductors having portions, such as 46, in contact with memory element40, and portions, such as 47, remote therefrom, with portions, such as50, to interconnect the portions 46 and 47. Such an arrangement canquite easily be provided using printed circuit techniques with portions46 on one side of a relatively thick board, and portions 47 on the otherside, and with overlaying holes through the board at the terminal endsof each portion, and interconnected with conductors, such as eyelets orrivets through the holes to provide the portions 50. If the circuitboard is of the order of 1/16 inch thick, the field in the ferromagneticsubstance, 42, due to conductor portions 47, will be at least four timesless than the field produced by conductor portions 46. This should besufficient to satisfy the requirement of producing discrete paths ofmagnetic domain alignment. And of course the circuit board can be madethicker than 1/16 inch. Again, it would be no great hardship to maketools that would punch and bend the conductor sets of FIGS. 6a and 6bfrom sheet material. In any event, when the multiplicity of magneticallyaligned parallel domain paths of a memory element label are attached toan article of goods in an activated state and presented in aninterrogation zone, a multiplicity of responses will be produced inphase agreement and the result will be much as if we had a multiplicityof separate ribbons any single one of which is able to produce a readilyidentifiable response, as proven by the apparatus in daily use undersome of the above referenced patents. Obviously, the magnitude of thetotal response of a memory element label, such as that if FIGS. 6a and6b, will be multiplied by the number of paths provided as long as theresponses are all in phase agreement.

Continuing with FIGS. 6a and 6b, 51 indicates the current conductorsabove described, 52 indicates arrows showing the direction of currentsin the conductors, 53 and 54 are buses which connect the conductors 51in parallel, while 55 and 56 are terminals to which a suitable EMF isapplied. 49 indicates a set of arrows pointing in the direction ofmagnetic saturation and domain alignment in ferromagnetic substance 42;48 points to the tips of arrows 49 in 42. 41 and 43 are the non-magneticlayers covering 42.

We go now to FIGS. 7a and 7b where the series arrangement of conductorsis worked out in detail. This essentially is a dual presentation of theconductors of FIGS. 6a and 6b, with the conductor portions, 67, adjacentthe memory element label, 60, of a first set of conductors, lined upopposite to the remote conductor portions, 70, of the alternating secondline set of conductors, and vice-versa. 69 indicates the conductorportions of the second line set of conductors adjacent the memoryelement label 60, and 68 indicates the remote conductor portions of thefirst line set. 74 points to the magnetic saturation, domain alignmentarrows produced by the first line set of conductors, while 75 points tothe arrows of magnetic saturation and domain alignment produced by thesecond set of line conductors. To better show the alternating adjacentand remote portions of the two sets of conductors, the second set ofline conductors is shown exploded away from the memory element label,60, in FIG. 7b, as indicated by the dotted lines. 76 points to the arrowtips of magnetic saturation and domain alignment in 62, and 77 points tothe arrow heads of alternating lines of saturation and domain alignment.71 is an arrow pointing generally to the series set of conductors; 72points to the arrows of current flow in the first set of conductors, and73 points to the arrows of current flow in the second set of conductors.78 and 79 are the terminals to which a suitable EMF is applied.

FIG. 8 shows the complete magnetic saturation domain alignment patternproduced by the conductors of FIGS. 7a and 7b. When a memory elementlabel attached to goods, and activated as shown by arrows 74 and 75, ispresented in an interrogation zone, one line set of magnetic saturationand domain alignment will respond primarily to one phase of aninterrogating signal while the second line set of magnetic saturationand domain alignment will respond primarily to an opposite phase of theinterrogating signal, as will be made clear subsequently.

In both the parallel line sets, and the series line sets, of magneticsaturation, FIGS. 6a and 7a, respectively, it is clear that the magneticsaturation will make line troughs through the ferromagnetic material,and adjacent these troughs, on either edge, will be parallel streaks ofdomain alignment.

Taking a second look at FIG. 8, the possibility of joining thealternating lines of magnetic saturation and domain alignment, to form asingle folded pole alignment of great length, comes to mind. If we canadd the pieces of magnetic saturation and domain alignment indicated bythe arrows 95 and 96, the alternating lines 74 and 75 can be joined.This can be accomplished by means of the conductor pattern of FIGS. 9aand 9b where conductor elements 83 adjacent memory label 60, on the leftside, and adjacent conductor elements 84, on the right side, are joinedby staggering the conductors one line position, as at 89. With currentspassed through these conductors, the appropriate pieces of saturationand alignment in the margins at both ends will be produced and, with alittle help from spontaneous polarization, the lines will be joined toprovide the overall saturation and domain alignment pattern of FIG. 10.If necessary, more complicated conductor arrangements can be provided atthe ends, but it is believed that designation of which lines are to bejoined, and which are to be kept separated, will be sufficient.Effectively, this makes one very long pole which becomes anexceptionally good absorber and radiator of energy in an interrogationzone, especially in view of the fact that energy can be absorbed fromboth phases of one wave period and delivered in one phase of anothertime period. Particularly will this be the case when the total lengthbecomes an appreciable fraction of a wave-length.

Considering the conductor configurations of FIGS. 7a, 7b, 9a and 9b froma practical point-of-view, it is clear that these can be accomplished bymeans of printed circuits on two sides of a printed circuit board ofappropriate thickness, or by means of die punched sets of conductors, aspreviously described. We turn now to the means taken to deactivate thememory element labels.

As is now broadly recognized, two magnetic states are required in anypractical anti-pilfering system, just as two magnetic states arerequired for the storage of information in any practical computer systemthat uses magnetic storage elements. In this respect, the fundamentalmemory requirements of anti-pilfering systems are no different than thefundamental memory requirements of computer systems. The only differenceis one of arithmetic. Whereas, a computer requires hundreds, orthousands, of memory elements for each function performed, ananti-pilfering system requires only one memory element for each functionperformed.

To activate a memory element label, parallel lines of magneticsaturation and domain alignment were provided along the long dimensionof the label by means of parallel current lines along the shortdimension of the label. To deactivate the memory element label, we nowprovide crossing lines of magnetic saturation along the short dimensionof the label by means of current lines along the long dimension of thelabel, as shown by FIGS. 11 and 12. FIG. 11 shows the arrangement ofconductors used to nullify the series activation configuration, and FIG.12 shows the arrangement of conductors used to nullify the parallelactivation configuration. While for convenience of exposition, we haveshown parallel lines of deactivation, it is recognized that deactivationmight be better accomplished if the lines were randomly spaced andoriented. Be this as it may, we'll proceed with the exposition as itpertains to the regularly spaced and oriented arrangements.

In FIG. 11, 10 points to the schematic arrangement of conductors,previously shown in FIGS. 3 and 7a, and here shown by dotted lines. 110points to the schematic arrangement of conductors, in full line, used todeactivate the memory element label. Heavy line segments 125 indicatethose portions of the activating conductor configuration 10 that areadjacent the label, while heavy line segments 126 indicate thoseportions of the deactivating conductor configuration 110 that areadjacent the label. Thus, each component of activation, saturation anddomain alignment is broken up by a crossing component of deactivation,saturation and domain alignment. Overall, this means that the memoryelement label, instead of being domain organized in a multiplicity oflong parallel lines, is broken up into a multiplicity of small domainareas which are ineffective in receiving and radiating energy in aninterrogation zone.

FIG. 12 shows a similar arrangement of deactivating conductors 120 usedto deactivate the pattern produced by the configuration 20, previouslyshown in FIGS. 4 and 6a. Heavy line elements 127 indicate the conductorelements of the network 20 adjacent the memory element label, whileheavy line elements 128 indicate the conductor elements of network 120that are adjacent the memory element label. As in FIG. 11, these lineelements are at right angles to each other as likewise will be theelements of magnetic saturation and domain alignment. In both FIGS. 11and 12, the crosses can be used to indicate the crossing currentelements, or the elements of magnetic saturation and domain alignment.

FIG. 13 shows a typical activate/deactivate head by means of whichmemory element labels can readily be positioned and activated ordeactivated as requirements dictate. Somewhat centered in the head isthe sensitive area 11 having the conductor patterns of FIGS. 11 and 12(not shown), as well as those of FIGS. 3 and 4 (also not shown), buthaving the location of the activate/deactivate points shown by thecrosses 101. This head is adapted to either pre-activate labels prior toattachment to goods or thereafter as may be required. When activation isaccomplished prior to attachment, the labels can be positioned in quicksuccession in the head and switch button 103 depressed. Prior topressing 103, however, selector switch button 104 is set to engage theactivate pattern of conductors in the head. If, on the other hand, wewish to deactivate the label, selector button 105 is set to engage thedeactivate pattern of conductors. An internal mechanism (not shown) isprovided to release 104 when 105 is engaged, and vice-versa. Means fordoing this are well-known to the push-button art and need not bedescribed here.

As is evident from the arrangement of FIG. 13, the label 40 can bepositioned in one of two perpendicular directions. This permits a choiceof which direction along the label the activation pattern isplaced--parallel with the length of the label or the width. Again, thelabel can be positioned as shown, or turned oppositely. Too, the labelcan be positioned face up, as shown, or it can be positioned face down.Altogether, a choice of eight positions are provided. With the positionsof activation and deactivation synchronized, a measure of security isprovided against the possible collaboration of crooks inside anestablishment with crooks outside. Unless the labels are identicallypositioned for activation and deactivation, the patterns wouldn'tcoincide so that an appropriate response would be made in aninterrogation zone. The cutaway, 102, in the label, shows thecontinuation pattern of crosses, 101, under the label.

When labels can be accurately placed in such things as books, areference frame comprised of frame members 106 and 107, which meet toform a right-angled corner, can be used. With this adaptation, thelabels would be accurately attached to either the front or back coversat prescribed distances from one corner, and these distances wouldcoincide with similar distances of the sensitive area, 100, from thereference frame corner provided by 106 and 107, so that when the bookwas appropriately positioned in the head, book label 40 and sensitivehead area 100 would coincide. In a similar way, other goods can bepackaged in cartons, boxes, plastic packages, etc., of fixed shapes,having labels in prescribed locations.

For less exacting applications, goods can be packaged in plastic bags orwrappings having visual memory element labels. Under this circumstance,a hand-operated stamp-like head, 90, as shown in FIGS. 14a and 14b,would be well suited. The crosses, 111, again show the locations of thesensitive spots; 112 is the frame of the hand-operated head, 113 is thehandle and 114 is a cable of electrical conductors which conveys thenecessary currents from auxiliary apparatus. 115 is the operating handleof a multi-position switch. In one position the conductors inside thehead are connected for activation; in a second position, the conductorsare set for deactivation. In use, the clerk-operator, having set switch115 for the action to be taken, would locate 90 over the memory label 1,40, or whatever, and press the operate button 116 with a finger. Thistype of apparatus is also adapted for use with unpackaged goods, such asarticles of clothing, which have visible memory element labels.

While deactivation has been described above in terms of unidirectionalpulses of current, the most effective means of deactivation is theapplication of alternating currents of appropriate frequencies and inenvelopes of exponentially decreasing amplitudes. When deactivation isaccomplished in this way, and the memory element labels can beaccurately positioned, the activating sets of conductors are all thatare necessary, and deactivation accomplished by applying the abovespecified alternating currents to them. When, however, the memoryelement labels cannot be accurately positioned with respect to theactivate/deactivate head, it is desirable to use both sets of conductorsand apply exponentially decreasing alternating currents of one frequencyto one set of conductors, and simultaneously apply exponentiallydecreasing alternating currents of a slightly different frequency, orphase, to the other set of conductors. In this way we'd get a rotatingpattern of deactivation so that it wouldn't matter particularly howskew, relatively, the placement of label and head might happen to be.The third position of switch 115, of hand-operated head 90, could, forexample, be used to provide this arrangement of conductors anddeactivating alternating currents. Similar arrangements could obviouslybe added to the head of FIG. 13.

As with all anti-pilfering systems, it is necessary to provide aninterrogation zone and this is usually located in a doorway or inconjunction therewith. For purposes of this invention, this part of theapparatus is shown schematically by FIG. 16 where 161 is a frame throughwhich customers pass and 162 is a loop of conductors supported by 161and connected at junctions a,b to other portions of the apparatus. 163is a signal generator wherein the various signal forms that are usedoriginate. The wave forms that can be used are rectangular pulses ofspecified widths and repetition rates, sawtooth pulses, square waves andcontinuous sinusoidal waves. 164 is a power amplifier, likewiseterminating into the junction a,b, and feeding power into loop 162whereby the signals generated by 163 establish an adequate magneticfield within the doorway 160 and surrounding interrogation zone. 165 isa selectivity apparatus, which also is connected to loop 162 at a,b, andby means of which the signals produced in memory element labels by themagnetic field of the doorway, are selected from the primary powersignals that are applied to loop 162, and from interfering noise thatalso might be found in the doorway and surrounding interrogation zone.The selectivity apparatus 165 passes the selected signals to amplifier166, where the signal level is raised to a desired value, and passed toanalyzing and registry apparatus 167. Several modes of operation arepossible, a few of which will be described with the help of the graphsof FIGS. 18, 19, 20, and 21.

If the interrogating power, originating in 163 and applied to loop 162by power amplifier 164, has the continuous square wave form of FIG. 18,and if memory element labels carried into the doorway are activated inthe pattern of FIG. 6a, responses of the form of FIG. 19 will beproduced, as best shown by making use of the hysteresis loops of FIG.15. Suppose that the memory label has ferromagnetic substance describedby the hysteresis loop 131, the activated rows of the label will be setat the retentivity point of the material, B_(r). If the component of themagnetic field in the doorway, intercepted by the memory element, andproduced by the positive half-cycle 181, is in a direction to drive thememory element back into, or toward, positive saturation in thedirection of arrow 143, the response, 183, will be relatively small. Onthe other hand, the negative half-cycle response, 184, as produced bythe pulse 182, will be relatively large because the memory element willbe driven from B_(r) in the direction of arrow 146 where a guidedmagnetic pathway of considerable length is available and whererelatively large amounts of magnetic energy can be stored. It is theenergy stored in the memory element that gives rise to the signal ofFIG. 19 when it is released by reflex action of the ferromagneticsubstance as it moves back to the stable minimum energy point, B_(r),when the drive is removed or reverses polarity. Because energy ismomentarily stored in the ferromagnetic memory substance, there is aphase delay of T₂ -T₁ seconds in the response of FIG. 19 with referenceto the driving wave of FIG. 18. If the driving wave of FIG. 18 isrepeated and continuous, the signal response of FIG. 19 will also berepeated and continuous. If, on the other hand, the drive is a sequenceof separated pulses, a sequence of separated pulses will be produced. Ineither case, the magnetic storage in the memory element label is readand appropriately analyzed by 167 in terms of how 167 has beenprogrammed. In computer terminology, this is a quite typicalnon-destructive read-out of a memory element.

Because a great multiplicity of memory paths of long length areprovided, the magnetic energy storage will be relatively large, ascompared with an unprocessed ribbon of material, and the signalresponse, resulting therefrom, large. High level gates can then be setto distinguish these signals from the much smaller responses producedafter the memory element label has been deactivated. Upon deactivation,each long magnetic path in the memory element is either completelydestroyed or broken into a multiplicity of short, crooked paths and theeffects obtained from long needle-like oriented magnetic domains lost.In other words, the magnetic moment of each long path has beendestroyed. In addition thereto, the demagnetization polarizations of thesimple dc-system will add small signal components that weren't therebefore. Making good use of the relative signal amplitudes, as well asthe content of the signals, the two conditions of the memory elementlabel can quite easily be distinguished--at least with the same accuracythat we read the "0" or "1" bits of a digital computer.

In addition to the foregoing deactivation procedures, the usual methodsof de-magnetization can be applied; i.e., passing the goods, with labelsattached, through exponentially decreasing alternating current magneticfields. When this has been done, the previously activated memory elementlabel is reduced to that of a relatively large single piece of materialof a poor shape with magnetic domains oriented in a multiplicity ofhit-and-miss directions. In this condition, it is a demonstrated factthat the response will be small and of a character that is different anddistinguishable from the response obtained from long thin strips whereinthe magnetic domains are mechanically oriented by the strip boundaries,or wherein the magnetic domains are oriented by the means disclosed inthis invention.

Obviously, the ferromagnetic markers of systems presently in use, asrepresented by the patents referenced above, can be further improved bythe methods and means of this invention. whereas, long ribbons offerromagnetic material have been provided, the same can effectively bemade even longer and thinner than they now are, or is mechanicallypractical, by applying the magnetic path division methods of thisinvention to them, and the signal levels now obtained from them raisedaccordingly. If the signals presently obtained are adequate, the powerof the doorway can be appropriately reduced or other simplifications ofapparatus and cost effected.

The alternating field demagnetization procedures above referenced can beapplied in the usual ways, as by passing the goods with their memorylabels attached through coils having alternating currents of appropriatefrequency and amplitude flowing in them. In view of the fact that thetangential component of the magnetic field issuing from a conductorcarrying electric current is utilized in this invention, another mostconvenient means of demagnetization becomes possible. Consider FIG. 17which shows a screen of conductors, 170, comprised of a multiplicity ofhorizontal conductors 171 and a multiplicity of lateral conductors 172.The conductors 171 terminate in buses 175 and 176, and terminals 177 and178, respectively, while the conductors 172 terminate in buses 173 and174, and terminals 179 and 180, respectively. If alternating EMF's areapplied to the pairs of terminals 177, 178 and 179, 180 currents willflow in conductors 171 and 172 and a tangential magnetic fieldestablished above and below the plane of the conductors. If goods, withmemory labels attached, are placed on this screen and EMF's ofappropriate frequencies and amplitudes applied to the terminal pairs177, 178 and 179, 180, the magnetization can be completely removed fromthe memory labels. As before proposed, the most desirable arrangement isto apply slightly different frequencies, or phases, to the terminalpairs, start with amplitudes sufficient to drive labels into magneticsaturation, and decrease more-or-less exponentially to the vanishingpoint over quite a few cycles--say 100 to 1,000 cycles. Obviously, thehigher the demagnetizing frequency, the less time is required inproviding an appropriate decrease in magnitude; at the same time, thefrequency must be low enough that skin-effect phenomena do notappreciably limit the depth of penetration of the magnetic field intothe ferromagnetic substance that is employed.

While the magnetic field intensity above and below the screen will notbe independent of the distance from the screen, as is true for thecorresponding electric field intensity in the electrostatic case, themagnetic field intensity will not change rapidly for distances above andbelow the screen that are small compared with the dimensions of thescreen. Thus, if the screen is hidden under a thinly-covered table topwhere goods are sold and packaged, as at a cashier's stand, and currentsof two slightly different frequencies automatically driven through themin the required envelope patterns, the magnetizing activation of thememory labels attached to the goods will be cancelled without anyoneknowing what has happened. The process in this instance is very similarto that of removing a recording from a magnetic tape. The onlydifference is that two frequencies are used and the dimensions have beenscaled up considerably.

When a customer has paid for his goods at the above described counter,where the memory labels are cancelled, and carries it through thedoorway 160, FIG. 16, nothing happens. When, however, a shopliftercarries stolen goods which haven't had memory labels cancelled at acashier's desk, through 160, signals are generated in, and radiatedfrom, the uncancelled labels, picked up in loop 162, selected in network165, amplified in 166, analyzed in 167, registered in whatever mannerprogrammed, and the shoplifter apprehended.

In the same way as above described for reading the magnetic activationof memory labels, 40, FIG. 6a, the memory labels, 60, of FIGS. 7a and 8can be read by probing them with the square waves and pulses of FIG. 18.In this situation, however, we have both positively and negativelypolarized storage grooves; consequently, if an equal number of positiveand negative grooves have been provided, the positive and negativesignal responses that are produced will be the same and an alternatingsignal, rich in harmonics, as shown in FIG. 20, will be produced. If weare phased as above described for FIG. 6a, the positive pulse 181,probing magnetic storage paths 74, FIG. 7a, will produce pulse responsessuch as 183, FIG. 19, and simultaneoulsy therewith, pulse 181, probingmagnetic storage paths 75, FIG. 7a, will produce pulse responses such as184, FIG. 19. The only difference is that, in the latter instance we areoperating from -B_(r). Please note, however, that we are probing withforward going MMF's in both instances, and arrows 141 and 142 movemagnetic flux in the same direction from -B_(r), to produce large signalpulse responses, as did arrow 143 from +B_(r), to produce small signalpulse responses. Accordingly, the small and large signal pulse responseswill be phased to add, resulting in the elongated pulse 185, FIG. 20.Similar results will be obtained when the magnetic memory paths areprobed by the pulse 182, FIG. 18, except that this time the combinedsignal pulse responses will be phased negatively, as 186, FIG. 20. Ifthe probing pulses, 181 and 182, FIG. 18, are continuously andsequentually applied, the signal pulse responses will be continuouslyproduced and received, and once more we have a good example of acontinuous non-destructive read-out from a memory element. But this isby no means all that can, or will, happen as will be seen when weexamine the magnetic storage pattern of FIG. 10 which results, as beforedescribed, when we add the magnetic continuation storage grooves, 95 and96, FIG. 8, as produced by the circuitry of FIGS. 9a and 9b, to thestraight line storage grooves 74 and 75, FIG. 8.

When the memory label 60', FIG. 10, is carried into an interrogatingfield and probed by the pulses of FIG. 18, much of the response ofmemory label 60, FIG. 8, will be produced; i.e., the signal pulseresponses of FIG. 20. But something else has been added. The positivelydirected magnetic grooves, 74, FIG. 8, have been joined by thenegatively directed grooves, to form the enormously long fieldcontinuous magnetic groove of FIG. 10. And while much, perhaps most, ofthe energy stored in this long groove by the probing pulses of theinterrogating field will be radiated out as individual components in themanner previously described, to produce a pattern such as that of FIG.20, some of the stored energy is bound to flow along the grooves, atleast the amounts required to fill the curved portions at the ends, tobe delivered later in the form of the pulse of FIG. 21. In other words,the magnetic domains which are moved by positive probing will beeffected by the magnetic domains that are moved by negative probing, andvica-versa. The great importance of this is that the pulse 187, FIG. 21,overlaps at least one full cycle of the probing pulse of FIG. 18. Inother words, the pulse of FIG. 21 will contain sub-harmonics of thepulse of FIG. 18. As far as it known, this is the first time such aresult has ever been achieved. And since sub-harmonics are never foundin nature, and are very difficult to produce, it is easy to see howvaluable this result can become in anti-pilfering devices.

The sub-harmonic response can be further augmented if steps areexercised to make the total magnetic path of FIG. 10 some appropriatefraction of a wave length, as a quarter of a wavelength, or a half of awave-length. The velocity of propagation of electromagnetic waves infree space is, of course, the velocity of light, c. In material media,however, the velocity is greatly reduced; indeed, the velocity ofpropagation is reduced by the factor ##EQU3## where μ is the magneticpermeability, and κ is the inductive capacity of the medium. Since ourmagnetic vector is confined to the plane of the memory element, andmostly to the lengthwise direction, we are concerned almost exclusivelywith the ferromagnetic substance and its close environs. Since also, thePoynting, or radiation, vector must be perpendicular to the plane of thememory element if energy escapes, or is radiated, therefrom, theelectric vector must also be in the plane of the memory element andperpendicular to the magnetic vector, which is to say along the width ofthe memory element.

Referring now to FIG. 2c, we can make 8 out of ferromagnetic materialhaving a permeability of 100,000, and we can make 7 and 9 out ofdielectric material, such as Titanium dioxide which has a dielectricconstant of at least 100. In this way, we can provide a product μκ=10⁷,or √μκ=3.16×10³. This means that the thirteen-line pattern of FIG. 10which totals about a meter in actual length, and which in free spacewould be one wavelength for a frequency of 300 megahertz becomes awavelength for 300/3.16 kilohertz, or 94.49 kilohertz. This is afrequency that falls within the range of what is presently practical inantipilfering devices of the type described in this invention.

With the folded magnetic groove length totalling a half-wave-length athalf the probing frequency, where the impedance would be minimum,conditions would be ideal for radiating energy at this frequency ascompared with the fundamental, or probing frequency, where the foldedmagnetic groove length would be a full wave-length and the impedancemaximum. This type of radiation system is a little bit like a helicalantenna although there are major differences. Whereas the helicalantenna is fed from one end and radiates broadside, the magnetic memorylabel of this aspect of the invention is fed broadside, and radiatesbroadside but from a magnetic domain coordinated length; i.e., each of amultiplicity of straight line paths receive energy from magnetic fieldof the doorway and, for the component of interest, give up energy alonga coordinated length.

Perhaps another way of looking at it is that the memory label of FIG. 10momentarily receives energy from the field faster than it can get rid ofit so that the energy accumulates over a primary cycle, or two, untilthe label can hold no more, then the label delivers energy back to thefield at some frequency most compatable with its construction, and thisshould be at some sub-harmonic frequency.

Considering the density of information on a magnetic tape recording, forexample, it is clear that the line density illustrated in FIG. 10 is byno means the greatest density that can be obtained. As far as theferromagnetic medium is concerned, the line density will be limited onlyby the cross-talk between lines; i.e., adjacent magnetic domainalignments affecting each other. From a practical manufacturingpoint-of-view, the line density will be limited by the conductor networkdimensions required to produce it. In any event, perhaps at least tentimes as many lines, or magnetic grooves, can be put in the same spaceshown by FIG. 10. If this can be done, the wavelength figure will bereduced by the same amount so that we could then get a total wavelengthfor the path at approximately 9.45 KHz.

In addition to reading the ferromagnetic memory label by means of thepulses, or square waves, of computer technology, it is of coursepossible to read the memory by means of continuous sinusoidal fields asis the practice of most anti-pilfering systems of the present day. Tothis end, 163, FIG. 16, would be a sinusoidal electric generator of anydesired frequency, 164 would be a suitable power amplifier for the same,165 would be an electronic filter of some sort, set to pass signals ofthe chosen frequencies, and exclude all others, 166 would be a suitablevoltage amplifier and 167 would be the analytic network or registerwhereby the signals received and passed by 165 and 166 are analyzed,compared, observed, etc. and used to provoke a necessary action asdetermined by the circumstances. The harmonic content of the receivedsignals, relative amplitudes of the odds and evens, etc., will bedetermined by the magnetic groove patterns of the labels presented inthe doorway, and the relative amplitudes of the harmonics used todetermine whether goods to which labels are attached arrive at thedoorway as a legitimate transaction or not. But the use ofdistinguishing harmonics to separate the legitimate and illegitimatetransactions becomes less of a necessity with the ferromagnetic memorylabels of this invention because the magnetic energy storage anddelivery has been so enormously multiplied as to make the relativeoverall signal amplitudes entirely adequate in separating the legitimatefrom the illegitimate transactions without reference to harmonics of onekind or another. In other words, the activated state of a label willproduce signals so enormously greater than the inactivated, orcross-activated, states as to provide in adequate system on the basis ofamplitude. This, too, we have not had before.

Referring again to FIGS. 16 and 16a, it is also possible to use theheterodyne methods of interrogation and signal separation with thelabels of this invention as were provided by one of the above namedreferences. To this end, we make 163 a generator of one frequency and169 a generator of another frequency, with 164 and 168 being suitablepower amplifiers in their respective channels, so that the magneticinterrogation fields are established simultaneously in the doorway. Thelabels being nonlinear devices, sum and difference frequencies will beproduced and picked up by loop 162, selected by 165 and thereafterhandled in the reception channel as required. As for other signal forms,the amplitudes of the sum and difference frequencies will be greatlyincreased by the memory labels of this invention, because the amounts ofenergy handled are greater.

With the exception of the exposition on the use of dielectric materialin combination with magnetic material to provide wavelength type labels,we have, thus far, considered a ferromagnetic substance comprised of onematerial, or one layer, as shown in FIG. 2a. While this is entirelyadequate for most applications, a further enhanced result can beachieved through the use of two layers of material, as shown in FIG. 2b,and as described by the hysteresis loops 131 and 132 of FIG. 15. Thematerial of loop 131 has high permeability and low coercivity while thematerial of loop 132 has low permeability and high coercivity, asalready noted. With suitable MMF's applied, the material of loop 131,under steady state conditions, will follow the arrows 142, 143, 144,145, 146, 147, 148, 149, 150, and 141. With the MMF removed at points ofpositive and negative saturation, arrows 144 or 149, and in the absenceof the material of loop 132, the material of loop 131 will fall back tothe points of retentivity, +B_(r) or -B_(r), respectively. The coercivepoints for this material are H.sub. 1 and H₃.

For the material of loop 132, the hysterisis loop, under steady stateconditions, is defined by the arrows 153, 144, 145, 154, 155, 156, 149,150 and 151. Upon positive or negative saturation, and in the absence ofthe material of loop 131, the material of loop 132 will fall back to theretentivity points +B_(R) and -B_(R), respectively, when the saturatingMMF is removed. The coercive points for this material are H₂ and H₄.

When both materials 131 and 132 are present together, and in intimatemagnetic contact, the initial operating points for activated materialwon't, however, be any of the points of retentivity, +B_(r), -B_(r),+B_(R), or -B_(R). For example, with both materials at positivesaturation, as depicted by arrow 144, and the saturating MMF removed,the material 131 wont't move back to B_(r), nor will the material 132fall back to B_(R). Rather, the high coercivity material will fall backto Y where it will drive negative flux through the low coercivitymaterial to pin it at a new operating point Y'. In essence, 132 is apermanent magnet and 131 it its keeper. In this way, each magneticgroove of the high permeability material, 131, is available to receivedoorway flux along an entire hysteresis length without running the riskof being destructively read. And when the doorway flux is removed, orgoes into an opposing cycle, the entire length of groove, or thatfriction of it used by doorway flux, gives up its momentarily storedenergy and falls back to Y'. Destructive read out will happen only whenthe applied MMF of the doorway flux exceeds the coercive values +H₂ or-H₄, and as is readily evident by taking a quick look at FIG. 15, thedoorway drive can ride around the entire hysteresis loop 131 withoutever exceeding these limits.

This operation is similar to that of a galvanometer coil operating in avery strong magnetic field. With current flowing in the galvanometercoil, the galvanometer needle rotates to a point defined by the currentin the coil, the strength of the magnetic field, and the restoring forceof the spring. With current in the coil removed, the needle and coil towhich it is attached gives up its energy and falls back to the zeroposition. And it is virtually impossible to put enough current throughthe galvanometer coil to de-magnetize the P.M. that produces themagnetic field in which the coil operates.

For oppositely polarized magnetic grooves, the operating line will beZZ' on the opposite, the right-hand side of the graph. Otherwise, theaction will be as above described. This combination of magneticmaterials gives us the best in magnetic path orientation and definition;that which is provided in a material of large coercive force; and thebest in signal response; that which is provided by a high permeabilitymaterial. This response can, however, be doubled by putting a layer ofhigh permeability material on each side of the high coercivity material,as illustrated in FIG. 2c.

While the methods and means above described for activating ferromagneticmemory labels, and as illustrated by FIGS. 6a, 6b, 7a, 7b, 9a and 9b,are entirely adequate, other means are of course possible. Three suchare illustrated by FIGS. 22, 23, 24, 25, 26, and 27.

FIGS. 22, 23, and 24 show activation method and means, 190, for moving aferromagnetic memory label 200 past two sets of conductors 201 and 202.One set, 201, is situated above the memory label 200, and the other set,202, is situated below. Five conductor bends, or portions adjacent 200,typified by 203, are in contact alignment on top the label, and fiveconductor bends, or portions adjacent 200, typified by 204, are situatedon the bottom, and these are separated and joined together by conductorportions remote from 200 and typified by 205 and 206, respectively. 211and 213 are the outer non-magnetic layers of the memory label and 212 isthe ferromagnetic layer. The thickness of the label is of course greatlyexaggerated for illustrative purposes. In practice, each layer of thelabel will be only a few mils thick so that conductor portions adjacentthe label, as 203 and 204, will set up strong magnetic fields in thelabel when current is passed through the conductors, as shown by FIG. 5and Equation (1). Accordingly, as the label is moved past conductor sets201 and 202, each of which carries at least half enough current tosaturate the ferromagnetic layer 212, parallel paths of saturation willbe established in the label. The conductor sets 201 and 202, FIG. 23,are connected in parallel and a suitable EMF applied to terminals 207and 208. Thus, this arrangement of conductors and transport system tomove the label, will produce the saturation flux pattern of FIG. 6a buthas the additional advantage of not depending upon spontaneous domainalignment to make the paths continuous. Obviously, it doesn't matterwhether the label moves with respect to fixed conductor sets, or whetherthe conductor sets move and the memory label remains fixed. Therequirement is that the length, or width, of the label be traversed bymagnetically segmented conductors carrying sufficient electric currentto saturate the ferromagnetic substance adjacent each such segment. Bymagnetically segmented conductors in this application, I mean thatarrangement of conductors having portions magnetically adjacent thememory label and portions magnetically remote therefrom, with saidadjacent and remote portions generally alternating with each other. Andby magnetically adjacent, I mean that the conductor is sufficientlyclose to the ferromagnetic substance that the tangential component ofmagnetic flux produced by current flowing in the conductor is sufficientto saturate the ferromagnetic substance. And by magnetically remote, Imean that the conductor is sufficiently far from the ferromagneticsubstance as to be unable to saturate the ferromagnetic substance.

Referring to FIGS. 23, 23 or 24 for some of the construction detailspassed by in the foregoing, FIG. 22 is the plan view of the arrangement,FIG. 23 is a cross-section of FIG. 22, looking in at AA', and FIG. 24 isan elevation of the structure of FIG. 22. 197 refers to the entirestructural framework of the device which, for simplicity, is made ofelectrically insulating material, such as plastic; otherwise, some means(not shown) must be taken to insulate the conductor sets 201 and 202from the framework 197. These conductor sets are mechanically positionedand supported by the frame and electrically insulated therefrom, asnoted, implicitly or explicitly as the case might be. 191, 192, and 193are the top rollers of a set of six which hold the memory label 200between them, and 198 is the central bottom roller. One, or more, pairsof these rollers are put in circular motion as indicated by the arrow220, by means not shown, so that the memory label 200 is driven past theconductor sets 201 and 202. The rollers are equipped with flanges, suchas 194 and 198, so that the memory label is guided by the edges as it istransported. 195 is a typical shaft by means of which each roller issupported in the frame 197, and 196 is a typical hub cap.

FIG. 25 is an alternate cross-section across AA' showing a variation ofthe conductor set patterns whereby memory paths of the form of FIGS. 7aand 8 are produced by means of the transport system and associatedapparatus. In this variation, the conductor sets are connected in seriesby means of the conducting bridge 223, and the application of a suitableEMF at terminals 221 and 222 on the opposite end. Also, one set ofmagnetically segmented conductors is arranged differently. The adjacentsegments, as 231, on one side of the memory label are opposite theremote segments, as 232, on the other side of the label, and vica-versafor 233 and 234. In this arrangement, each conductor segment carriesenough electric current to saturate the ferromagnetic substance of thelabel, as compared with half enough in the arrangement of FIG. 23. Sincethe currents in one set of conductors, on one side of the label, flow inopposite directions to the currents in the other set of conductors, onthe opposite side of the label, alternate paths of magnetic saturationwill be set up in the label, as in FIGS. 7a and 8.

FIGS. 26 and 27 show how a set of magnets, permanent or electro-, can beused in a transport system to set up lines of magnetic saturation in amemory label. We'll assume that the transport system of FIGS. 22 and 24,or the equivalent thereof is used, and that the framework, 197, of thetransport system, supports and positions the system of magnets withrespect to the memory label 200. In the simplest arrangement, each ofthe teeth, as 217 and 218, are little P.M's. which are set into theyokes 214 and 215. The 217 P.M's. have North poles protruding and arearranged above the memory label, while the 218 P.M's. have South polesprotruding and are arranged below the memory label with a shortdisplacement parallel with the label. Thus, in the gap between poleteeth, magnetic flux will flow through the ferromagnetic substance ofthe label, as shown by the arrow 219, and if of sufficient strength willsaturate the ferromagnetic substance between each pair of pole teeth sothat as the memory label is transported past the teeth saturation lines,and domain alignment, will be established in the ferromagnetic substanceof the memory label.

End yokes, 209 and 210, not shown in complete detail, provide for theflow of return flux. Suffice it to say, for the purpose of thisinvention, that these yokes pass diagonally across each end.

If we wish parallel lines of saturation, all flowing in one direction,as in FIG. 6a, we cause all of the poles of one set of magnet teeth, onone side of the card, to have the same polarity, and the set of magnetteeth, on the other side of the card, to have the opposite polarity. Asalready stated, we can use individual P.M. teeth; alternatively, we canplace P.M.'s in each of the yokes, 209 and 210, with the poles of bothset in the same direction.

On the other hand, if we wish to establish alternating lines of magneticsaturation and domain alignment, as in FIGS. 7a and 8, we alternate themagnetic poles on each side of the memory label and arrange it so that aNorth pole on one side of the label is opposite a South pole on theother side of the label. We also design to have our pole spacing suchthat the separation of poles on each side of the label is great comparedwith pole separations through the label. Considering that the drawingviews greatly exaggerate some dimensions, so that the principles of theinvention can be clearly seen, this can quite easily be done. The memorylabel is only a few mils thick, as before stated, and the toothstaggering on opposite sides of the label need not be more than a fewmils, it is quite possible to have adjacent pole teeth on each side ofthe label at least ten times further apart than are pole teeth throughthe label.

To employ electromagnetic techniques in each instance, we canappropriately apply electrical windings to the magnet system, in eachinstance, the entire structure of each of which is now made out of softferromagnetic material. For the parallel line case of FIG. 6a, we simplyput electrical windings around each of the yokes 209 and 210, and directthe currents in each winding to produce opposing magnetic fields. Forthe series case of FIGS. 7a and 8, we are obliged to put windings aroundthe individual teeth much like we would wind an electric motor. This canbe done in honeycomb, ring-around-the-rosy fashion, or individual coilscan be placed around each tooth and connected externally to provide thedesired polarities, as given above for the P.M. case.

What is claimed is:
 1. A electronic status determining label for goodsin sheet form, responsive to a magnetic field varying at a predeterminedfundamental frequency, said label providing for the storage of no morethan two bits of information and comprising at least:a sheet offerromagnetic substance having active and inactive states; said activestate comprised of a multiplicity of long magnetically saturated lines,or grooves, on either side of which is non-saturated ferromagneticmaterial; said inactive state provided in one of two ways:the absence ofa multiplicity of long lines of magnetically saturated lines, orgrooves, said ferromagnetic substance being magnetically uniform andunmagnetized throughout; or by crossing lines of magnetic saturationwhich break the sheet of ferromagnetic substance into a multiplicity ofsmall areas.
 2. An electronic status determining label for goods, as inclaim 1, said ferromagnetic sheet having a thickness dimension at least100 times smaller than the other two dimensions which differ by lessthan a factor of
 5. 3. An electronic status determining label for goods,as in claim 1, wherein said ferromagnetic substance is sandwichedbetween layers of thin non-magnetic material.
 4. An electronic statusdetermining label for goods, as in claim 1, wherein the ferromagneticsubstance is comprised of one material having an unique hysteresis loopby means of which it can be identified.
 5. An electronic statusdetermining label for goods, as in claim 1, wherein the ferromagneticsubstance is comprised of two materials, each of which is in a thinlayer in magnetic contact with the other layer throughout the extent ofboth layers, each of said two layers having unique hysteresis loops bymeans of which each can be identified.
 6. An electronic statusdetermining label for goods, as in claim 5, wherein one layer and onematerial has high permeability and low coercivity, and wherein the otherlayer has low permeability and high coercivity.
 7. An electronic statusdetermining label for goods, as in claim 1, wherein the ferromagneticsubstance is comprised of two materials and three layers with first andthird layers having high permeability and low coercivity, and sandwichedbetween them a second layer having low permeability and high coercivity.8. An electronic status determining label for goods, as in claim 1, saidlong lines of magnetic saturation all having the same polarity.
 9. Anelectronic status determining label for goods, as in claim 1, said longlines of magnetic saturation having alternating polarities.
 10. Anelectronic status determining label for goods, as in claim 9, whereinsaid long lines of alternating polarity saturation are joined atalternate ends to form one long folded path of magnetic saturation.